1. Field of the Invention
The present invention relates to a forward (downlink) packet scheduling method and apparatus in a base station of a portable Internet system, and more particularly, the present invention relates to a forward packet scheduling method and apparatus in a base station of an IEEE 802.16 Wireless MAN-based portable Internet (WiBro) system.
2. Description of the Related Art
The IEEE 802.16 Wireless Metropolitan Area Network (MAN)-based (WiBro) system is a 3.5 Generation mobile communication system providing image and high-speed packet data transmission such as various IP-based wireless data services (streaming video, mail, chafting) that the wired Internet provides, using a wireless transmission technology ensuring a spectrum use efficiency in a 2.3 GHz frequency bandwidth.
FIG. 1 is a schematic diagram of a conventional portable Internet (WiBro) system.
As shown in FIG. 1, a WiBro (Wireless Broadband) system includes a user terminal (also known as Access Terminal or “AT”) for using a portable Internet service, a base station 20 (also known as Access Point or “AP”) supporting a wireless access and network connection between the user terminals 10, and a packet access router 30 (“PAR”) for performing an each-terminal mobility control and packet routing function.
The user terminal 10 may receive a wireless data service after the user terminal is recorded at the base station 20. In addition, the user terminal 10 may configure a plurality of traffic connections having different Quality of Service (QoS) requirements through a negotiation with the base station 20 so as to connect services having different service characteristics such as a web connection and FTP.
The base station 20 performs access control of the user terminal 10, packet mapping between the wired and wireless areas, wireless transmitting/receiving control, and wireless band management.
The packet access router (PAR) 30 performs an each-user-terminal mobility control and packet routing function.
The WiBro system transmits/receives data every frame so as to support high speed packet data transmission in the wireless area, and is operated based on an OFDM/FDMA/TDD (Orthogonal Frequency Division Multiplexing/Frequency Division Multiple Access/Time Division Duplex) wireless transmission scheme.
FIG. 2 is a schematic diagram of a wireless frame of a portable Internet (WiBro) system.
A frame includes a downlink (DL) frame and an uplink (UL) frame. The respective frames transmit a MAP message including frame configuration information at the leading part thereof and then transmit a data burst. Therefore, a scheduler for performing wireless management allocates/manages a sub-channel so as to transmit the respective user data every frame and configures a MAP message based on the sub-channel-related information.
The MAP message includes a DL-MAP for downstream traffic and a UL-MAP for upstream traffic, and each MAP includes a GMH (Generic MAC Header), IE (Information Element) informing data burst information, and CRC (Cyclic Redundancy Check). The IE defines a data region, stores each data region information (which are needed in each data region), and informs of each data region information.
Among the respective IEs, Normal DIUC (DL Interval Usage Code) IE, Hybrid Automatic Repeat Request (HARQ) DL MAP IE, Normal UIUC (UL Interval Usage Code) IE, HARQ UL MAP IE, etc. refers to data burst contents and includes information about which user receives the same or similar information.
The uplink frame includes Channel Quality Indicator Channel (CQICH), Acknowledge Channel (ACKCH), and Code Division Multiple Access (CDMA) ranging in an uplink control symbol (UL control symbol). A CDMA ranging channel includes information for a random access using CDMA code, the CQICH ranging is for adaptive modulation, and the ACK is ACK information for HARQ.
According to the OFDM/FDMA/TDD scheme, data transmitting/receiving is performed by a sub-channel, wherein the sub-channel is configured by a sub-carrier group. In addition, the respective frames transmit a MAP message including frame configuration information at the leading part thereof and then transmit a data burst (the burst being a set of Packet Data Units (PDUs) to be transmitted for the respective users, and the same radio channel parameter is used so as to transmit a single burst). Therefore, the base station 20 for performing wireless management allocates/manages a sub-channel to transmit/receive the respective user data every frame, configures the MAP message based on the sub-channel concerning information, and the user terminal 10 receives the MAP message, receives the upstream/downstream data burst information allocated to the base station, and transmit/receives the corresponding data burst.
Generally, in almost all wireless communication systems, the overall efficiency or transmission characteristics thereof largely depends on which scheduling algorithm is used. Therefore, a scheduling algorithm may be chosen according to usage. Representatively, a method for maximizing system transmission efficiency and a method for ensuring fairness between the terminals have been proposed.
The first method can maximize system throughput because almost all radio resources are allocated to the terminal having the best channel state. However, there is a problem in that the terminal having a poor channel state may have sufficient service because the radio resources are not allocated regardless of a large amount of data to be transmitted.
The second scheme can fairly allocate a radio resource to all terminals regardless of the channel states because it uniformly allocates radio resources to all the terminals. However, the second scheme has a drawback in that the system throughput may be decreased because a large amount of resources is allocated to terminals having a poor channel state. That is, these two methods each have a fatal drawback. Therefore, recently, wireless systems prefer a proportional-fairness (hereinafter, called “PF”) scheme for enhancing system throughput by means of a system throughput/fairness trade-off. However, the PF scheme has a drawback in that each user's different QoS requirements and real-time service are not considered.
The conventional wireless communication system supports a single service. However, the WiBro system supports various multi-media services such as a real-time service, a non-real-time service, and the newest service. Therefore, the WiBro system requires scheduling considering each service's QoS requirements. In addition, the scheduler of the WiBro system must determine a proper MCS (Modulation and Coding Scheme) level based on the user channel state according to the requirements of the system applying an AMC (Adaptive Modulation and Coding) scheme so as to ensure wireless transmission. In order to easily realize the WiBro system as well as to solve the above-described problems, scheduling must be performed before frame synchronization because frame synchronization is exactly matched to satisfy the frame-based WiBro system operation conditions and system performance, and a minimum process time must be ensured because the MAP message is configured.